Harvard University, like many universities and colleges throughout the United States, advises its students to use the Modern Language Association style guide for research (or reference) papers in English, history, and other classes in the the liberal arts category. The MLA's style guide is titled MLA Handbook for Writers of Research Papers, and is available from many sources, including on-line sites. This guide covers all aspects of writing research papers in the humanities--from how to do research to how to quote and create proper citations for your sources. The MLA style format is probably used by ninety percent of the universities and colleges in the US.
For research or reference papers in subjects other than English, history, art, political science, and other humanities courses, many schools, including Harvard, require research papers to be in what is called the APA format, which stands for the American Psychological Association style manual--again, this is available from many sources in print and on-line. The APA and MLA formats are substantially similar, but the APA format requires a slightly different organization for the research paper. For example, the APA style requires a summary of the paper at the beginning called the Abstract. The MLA format does not require an abstract.
Several schools in the United States, most notably the University of Chicago, require that research papers in all subjects follow what is called the Chicago Manual of Style, which was developed by the University of Chicago Press and then was adopted by the university. Most journals and scholarly publications published in the US require articles to follow MLA format, but there are a number that require the Chicago Manual.
Almost all colleges and universities in the US instruct students in which research paper style manual to follow, but as I said, most schools in this country use the MLA and APA formats.